I have an old house, I would like to build a new one on the existing foundation making sure it is energy efficient because of the cold winters we have, how do I do it?
A:
First things first, I would recommend that you completely remove the foundation using an excavator and then have a new foundation installed in its place. That is actually more cost effective then removing the wood structure off the top and reusing the existing foundation.
Since that’s not the question that you asked me here is what you need to do to save your older foundation and place a new home on top.
1. You must have an engineer look at the foundation and the cracks that are currently in it. If you are going to remove the wood structure from the top you really should also take of the old floor, the problem is that the old floor is helping hold up the concrete foundation. The ground that is piled up on the outside of the foundation is putting pressure inwards on the foundation and the floor is helping hold the concrete from being pushed inward. The engineer will be able to tell you if the foundation will hold up if you remove the structure off the top or if you need to leave the floor to help brace the walls.
2. Because it’s an older foundation you will need to dig around the entire foundation and re-waterproof it. Since it’s an older foundation you might as well install a new drainage tile around the outside of the home and run it into the house to the existing or new sump pit. Then you have to cover the drainage tile with gravel before you backfill with either sand or stone. This will help make sure that your foundation does not have an excess of water around it that could cause it to leak.
3. Insulating the basement can be done in many different ways. I would recommend that you spray foam all the walls downstairs, the spray foam will seal the walls from the cold outside, you can also foam the wood rim joist while your at it (once the new structure has been built on top). You have to cover the spray foam with something because it is a flammable product, you have two options; The first is you have the insulation company spray a fire retardant overtop of the foam, the second is that you frame stud walls up and then spray foam between them allowing you to cover it with drywall afterwards.
4. If there isn’t a concrete floor in your existing basement then you should install one. Before you install the new concrete you should place 4 to 6 inches of stone overtop of the existing ground, install a vapour barrier and then a layer of polystyrene insulation over top of that. This will help keep your basement warm and dry and also limit the heat loss in the winter.
5. If there is a concrete floor already in your basement you should assess if it’s worth keeping. You have to check to see what shape the concrete is in, is it cracked, broken, heaved? Also if your new building requires you to install more load bearing footings or pads then you will be removing some of the existing concrete anyways. Since your already going to the trouble of having the existing foundation saved you might as well remediate the basement floor so that you do not have any problems down the road.
6. With the removal of the building above taken all the pressure off the foundation you can alter the foundation quit easily. If you want to make the new house larger then now is the time to add an addition, adding a new concrete foundation extension is quite easy, so is the joining in to the old foundation. If you wanted to add windows to the foundation or an outside entrance then now is the time, you can add in the headers to spread the weight above it when you frame the new house. The more windows you are able to add to the basement the less it will feel like a basement.
7. Depending on the height of the foundation you can actually make the basement taller. There are two ways you can do this; The first is that you frame a knee wall on top of the existing foundation, this will take a basement that is only 6’5 to 8 or 9 feet high. The second way is to dig down past the existing footings and install in ones and a new concrete wall that extends down two or three feet. This will also give you a full height basement, full height basements add livable square feet without increasing the overall size or footprint of the home. It is easier to heat livable square feet in the basement then it is in the upstairs because the ground temperature doesn’t change as quickly or as often as the air temperature does.
8. In the basement make sure that the heating contractor installs heat and cold air returns. You want the air to be exchanged in the basement the same way it is exchanged in the rest of the house. If you want to use the basement you must treat it like any other part of the home.
9. To help a basement that might be short on height I always recommend that you install pot lights in the basement. The pot lights help give the illusion of higher height ceilings giving the that added head height. Instead of installing pot lights with halogen bulbs spend a little extra money and have them install pot lights that will except LED bulbs. LED bulbs use 1/10th of the power that halogens use and last 20 times as long, they are also much brighter and more adapt to lighting up darker parts of the home like the basement.
When re using an existing foundation your contractor will have too take care that his framing ends up tight to the foundation and that the insulators take the time to get all those hard to reach places. This will cut down on any drafts or heat loss in the cold winter. Nothing wastes more energy than a cold draft.
Rob Abbott
Operations Manager
Village Builders Inc.
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